1. Field of Inventions
Embodiments of the present invention generally relate to a marine craft. Preferred embodiments relate to the stabilization of marine craft by minimizing rolling and/or pitching motion. Further still, embodiments relate to the use of a spinning liquid mass in order to minimize oscillation in a marine vessel.
2. Description of Related Art
A gyroscope mounted with its single gimbal axis orthogonal to the major axis of a ship serves to limit rolling motion. Further, a gyroscope mounted with the gimbal axis parallel to the major axis of the ship reduces pitching motion. The gyroscope uses angular momentum and precession to counter these oscillations. Larger vessels require a larger gyroscopic system that can provide greater stabilization forces, while smaller vessels may employ a smaller gyroscopic system.
The utility of gyroscopes as a means of stabilizing watercraft has been known for many years. Stabilization increases passenger comfort and safety, reduces wear and tear on equipment, and increases the accuracy of warship artillery. An early gyroscope patent is U.S. Pat. No. 1,150,311, which issued in 1915 to inventor Elmer A. Sperry. The '311 patent was entitled “Ship's Gyroscope.” Mr. Sperry's gyroscope employed a large, solid spinning mass that precessed about gimbal bearings. The gimbal bearings were connected to a frame. The frame, in turn, was operatively connected to the hull of a ship.
Mr. Sperry's gyroscope was utilized by the U.S. Navy as an early gyro-stabilizer system. According to one publication, the gyro was installed aboard a small 700 ton destroyer, and in a submarine. Using the centrifugal motion of the spinning mass, gyrsoscopic forces were transmitted to the hull of the naval vessels through the gimbal axis. Depending upon the orientation of the gimbal axis, the gyroscopic forces could stabilize a floating vessel either as to pitch or as to roll.
Mr. Sperry's gyroscope was “active” in operation, rather than “passive.” In this respect, the Sperry gyroscope used a small gyroscope that sensed the onset of rolling motion. This small gyroscope was electrically connected to the switch of a motor that actuated a precessional gear mounted on a much larger gyroscope. A small gyroscope is more sensitive to rolling motion at inception than a large gyroscope. By activating the motor connected to the precessional gear of the large gyroscope, the large gyroscope was forced to precess at the moment it was needed. Further the motor can increase or decrease the angular velocity of precession to increase or decrease the stabilizing torque as needed based on the magnitude of the external torque. This “active” gyroscope system is preferable in many cases to a “passive” system because the rotor on an “active” gyroscope can be smaller.
Stabilizing torque of a gyroscope is a function of several factors. These include mass of the flywheel, or “rotor,” angular velocity of the rotor, radius of the rotor, and angular velocity of precession of the rotor when subject to an external torque. In order to provide stabilization for a large vessel such as a war ship, Mr. Sperry's ship gyroscope was required to utilize a large metal rotor having a great deal of mass. According to one publication, Mr. Sperry's gyroscope as utilized by the U.S. Navy weighed 5 tons.
The manufacture of such a device was and remains understandably expensive. In addition, the added weight of the gyroscope increases the fuel consumption of the vessel when in transit. As a result, technologies such as the “active fin” system were developed after World War I to utilize gyroscopic forces in a more indirect manner, permitting the use of smaller gyroscopes. The fin method was preferred to Sperry's ship gyroscope in part due to the much lower weight requirement. Additional background can be found in U.S. Pat. No. 3,389,674 to Pratt, U.S. Pat. No. 2,104,226 to Gonzales, DE 11 01 205 to Salomon, SU 1,601,022 to Moscovskii Avtomobilno Dorozhnyj Institute as reported in Derwents, U.S. Pat. No. 2,953,925 to Yeadon, FR 2 220 416 to Alsthom and JP 54 124494 to Ishikawajima Harima Heavy Ind. Co. Ltd. as reported in Patent Abstracts of Japan.
The use of active fins to reduce roll continues today. The active fin system works using a small gyroscope that senses rolling motion and sends a signal to move hull-mounted external fins that counter the motion. However, the active fin system requires that the ship be moving. The active fins are of no value in eliminating oscillations of marine vessels that are at rest. In order to eliminate oscillations of a ship at rest, one or more larger gyroscopes operatively connected to the ship's hull would have to be reintroduced. This has generally proved to be impractical and/or cost-prohibitive.
An important activity that requires stabilization of marine vessels that are at rest is the extraction and transport of hydrocarbons. A few examples of such vessels are membrane liquefied natural gas (LNG) tankers, offshore workboats, drill ships, floating production storage and offloading vessels (FPSO's), catenary anchor leg mooring buoys (“CALM” buoys), and oceanographic survey vessels.
Membrane LNG tankers cannot be loaded or offloaded in certain sea states, as excessive roll and pitch motion creates sloshing of liquid within the tanker. Excessive sloshing of large volumes of LNG can cause damage to the containment tanks. Because of this, LNG tankers must postpone loading or offloading when certain heavy seas are forecast. Therefore, a method to stabilize LNG tankers during loading or offloading would increase the integrity of these vessels and reduce vessel standby time.
Offshore oil and gas platforms need frequent resupply from land. This resupply is performed using workboats that tie up to the platform while a crane is used to transfer supplies to the platform. The transfer becomes increasingly difficult and hazardous as seas become rough. Thus, stabilization of the workboat is desired.
Drill ships oftentimes operate in rough seas. Weather and marine forces act against drill ships to reduce their operability. A particularly difficult operation in rough seas is the movement of large stands of vertical pipe into and out of a borehole. In addition, while drilling proceeds the drill pipe travels from the drilling rig down to the seafloor inside a riser pipe. Excessive rolling motion of the ship can cause the drill pipe to contact the riser pipe. This contact, and extreme motion in general, increases the risk of failure of the riser and equipment stress/fatigue in general. Thus, stabilization of drill ships will increase their operability and integrity.
Floating production storage and offloading vessels (FPSO's) typically remain moored for long periods of time. The natural oscillatory motion applied by the ocean to these vessels increases the rate of fatigue of mooring lines and other equipment. Also, large motions can decrease the efficiency of certain oil-water separation equipment that require quiescent conditions. A large vessel stabilizing gyroscope installed on an FPSO would decrease equipment fatigue and increase oil-water separation efficiency.
Mooring line fatigue is also an issue with buoys, such as catenary anchor leg mooring buoys, known as “CALM” buoys. Thus, stabilization of CALM buoys is desired.
Oceanographic survey vessels require stability during certain critical measurements. Likewise, seismic vessels need stability during operations.
Stabilization is also desirable in rescue craft and pleasure boats. Placement of an appropriately-sized gyroscope would aid in providing treatment and comfort to a rescued worker, and would minimize debilitating sea sickness of all passengers. However the placement of solid mass gyroscopes in smaller vessels is not always practical.
High-speed boat racing is a particularly hazardous activity. It is not uncommon for these boats to lose control and become airborne. This result occurs when control of the attitude of the boat is lost in choppy water. Those of ordinary skill in the art will appreciate that “attitude” refers to the orientation of a craft relative to the direction of its motion. A gyroscope mounted along the hull of a racing boat would act to maintain the attitude of a racing boat while the boat is in motion. It would do this by countering the forces that would act to change the boat's attitude at inception when these forces are still weak. Thus, an appropriately designed gyroscope could increase the integrity of high-speed racing boats.
Therefore, there is a need for a gyroscopic system that can provide stabilization of marine vessels even while the vessel is not being propelled. Further, there is a need for such a system that is relatively lightweight during manufacture and installation. Still further, there is a need for such a system that utilizes abundantly available seawater as the spinning mass during operation. Finally, there is a need for such a system that is capable of offloading the seawater when the vessel is moving, thereby minimizing fuel usage.